Eastern gray squirrels produce moans for aerial predators and quaas for terrestrial threats. One commonly-supported hypothesis for such predator-associated signals is that they elicit predator-specific escape responses in conspecifics. With simulated aerial predators, squirrels ran to the far side of tree trunks. In response to simulated terrestrial predators, squirrels frequently ran to where they could see the predator but could quickly flee to the far side of the tree trunk. Playbacks of quaas and moans elicited flight behaviour, but without association between escape location and alarm call type. Locations elicited by alarm calls differed from those elicited by simulated predators, with squirrels pausing on the side facing the call’s source. While grey squirrel alarms and escape strategies differ by predator type, the vocalizations do not function to elicit divergent escape strategies in conspecifics. This result stands in contrast to observed functions in other species with calls differing by predator type.

DigweedS.M.RendallD. (2009b).
Predator-associated vocalizations in North American red squirrels (Tamiasciurus hudsonicus): to whom are alarm calls addressed and how do they function? —
Ethology115:
1190-1199. DOI:10.1111/j.1439-0310.2009.01709.x.

MacedoniaJ.M. (1990).
What is communicated in the antipredator calls of lemurs: evidence from playback experiments with ringtailed and ruffed lemurs. —
Ethology86:
177-190. DOI:10.1111/j.1439-0310.1990.tb00428.x/abstract.

Figures

Three categories of location on trunk relative to threat. This diagram represents the view from above immediately after a stimulus object has stopped moving. The circle represents the trunk of a tree in cross-section, with the two intersecting lines dividing its surface into four quadrants. A squirrel could flee to any of four quadrants on the trunk surface, which were classified into three categories: (A) near, the quadrant of the tree facing the stimulus; (B) midway, the two quadrants midway around the tree trunk relative to the stimulus; (C) far, the quadrant farthest from the stimulus object, with the trunk between the squirrel and the stimulus.

Time to reach tree trunk in response to aerial versus terrestrial stimuli. Focal squirrels’ latencies to reach the trunk after release of the stimulus object differed based on stimulus type (MWU exact test: U=128, p<0.0001). Latencies to reach the trunk were shorter in response to aerial stimuli (N=33) than in response to terrestrial stimuli (N=36).

Three categories of location on trunk relative to threat. This diagram represents the view from above immediately after a stimulus object has stopped moving. The circle represents the trunk of a tree in cross-section, with the two intersecting lines dividing its surface into four quadrants. A squirrel could flee to any of four quadrants on the trunk surface, which were classified into three categories: (A) near, the quadrant of the tree facing the stimulus; (B) midway, the two quadrants midway around the tree trunk relative to the stimulus; (C) far, the quadrant farthest from the stimulus object, with the trunk between the squirrel and the stimulus.

Time to reach tree trunk in response to aerial versus terrestrial stimuli. Focal squirrels’ latencies to reach the trunk after release of the stimulus object differed based on stimulus type (MWU exact test: U=128, p<0.0001). Latencies to reach the trunk were shorter in response to aerial stimuli (N=33) than in response to terrestrial stimuli (N=36).